Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754187Ab3HXKQ3 (ORCPT ); Sat, 24 Aug 2013 06:16:29 -0400 Received: from mail-qc0-f177.google.com ([209.85.216.177]:55166 "EHLO mail-qc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753345Ab3HXKQ2 (ORCPT ); Sat, 24 Aug 2013 06:16:28 -0400 MIME-Version: 1.0 In-Reply-To: <20130819160425.310264395@infradead.org> References: <20130819160058.539049611@infradead.org> <20130819160425.310264395@infradead.org> From: Paul Turner Date: Sat, 24 Aug 2013 03:15:57 -0700 Message-ID: Subject: Re: [PATCH 04/10] sched, fair: Shrink sg_lb_stats and play memset games To: Peter Zijlstra Cc: Ingo Molnar , Joonsoo Kim , LKML , Mike Galbraith , Alex Shi , Preeti U Murthy , Vincent Guittot , Morten Rasmussen , Namhyung Kim , Lei Wen , Rik van Riel , Joonsoo Kim Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5011 Lines: 113 On Mon, Aug 19, 2013 at 9:01 AM, Peter Zijlstra wrote: > We can shrink sg_lb_stats because rq::nr_running is an 'unsigned int' > and cpu numbers are 'int' > > Before: > sgs: /* size: 72, cachelines: 2, members: 10 */ > sds: /* size: 184, cachelines: 3, members: 7 */ > > After: > sgs: /* size: 56, cachelines: 1, members: 10 */ > sds: /* size: 152, cachelines: 3, members: 7 */ > > Further we can avoid clearing all of sds since we do a total > clear/assignment of sg_stats in update_sg_lb_stats() with exception of > busiest_stat.avg_load which is referenced in update_sd_pick_busiest(). > > Signed-off-by: Peter Zijlstra > --- > kernel/sched/fair.c | 42 +++++++++++++++++++++++++++++++++++------- > 1 file changed, 35 insertions(+), 7 deletions(-) > > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4282,12 +4282,12 @@ static unsigned long task_h_load(struct > struct sg_lb_stats { > unsigned long avg_load; /*Avg load across the CPUs of the group */ > unsigned long group_load; /* Total load over the CPUs of the group */ > - unsigned long sum_nr_running; /* Nr tasks running in the group */ > unsigned long sum_weighted_load; /* Weighted load of group's tasks */ > unsigned long load_per_task; > - unsigned long group_capacity; > - unsigned long idle_cpus; > - unsigned long group_weight; > + unsigned int sum_nr_running; /* Nr tasks running in the group */ > + unsigned int group_capacity; > + unsigned int idle_cpus; > + unsigned int group_weight; > int group_imb; /* Is there an imbalance in the group ? */ > int group_has_capacity; /* Is there extra capacity in the group? */ > }; > @@ -4303,10 +4303,38 @@ struct sd_lb_stats { > unsigned long total_pwr; /* Total power of all groups in sd */ > unsigned long avg_load; /* Average load across all groups in sd */ > > - struct sg_lb_stats this_stat; /* Statistics of this group */ > struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */ > + struct sg_lb_stats this_stat; /* Statistics of this group */ > }; > > +static inline void init_sd_lb_stats(struct sd_lb_stats *sds) > +{ > + /* > + * struct sd_lb_stats { > + * struct sched_group * busiest; // 0 8 > + * struct sched_group * this; // 8 8 > + * long unsigned int total_load; // 16 8 > + * long unsigned int total_pwr; // 24 8 > + * long unsigned int avg_load; // 32 8 > + * struct sg_lb_stats { > + * long unsigned int avg_load; // 40 8 > + * long unsigned int group_load; // 48 8 > + * ... > + * } busiest_stat; // 40 56 > + * struct sg_lb_stats this_stat; // 96 56 > + * > + * // size: 152, cachelines: 3, members: 7 > + * // last cacheline: 24 bytes > + * }; > + * > + * Skimp on the clearing to avoid duplicate work. We can avoid clearing > + * this_stat because update_sg_lb_stats() does a full clear/assignment. > + * We must however clear busiest_stat::avg_load because > + * update_sd_pick_busiest() reads this before assignment. > + */ Does gcc seriously not get this right if we just write: sds->busiest = NULL; sds->local = NULL; .... etc.? > + memset(sds, 0, offsetof(struct sd_lb_stats, busiest_stat.group_load)); > +} > + > /** > * get_sd_load_idx - Obtain the load index for a given sched domain. > * @sd: The sched_domain whose load_idx is to be obtained. > @@ -4665,7 +4693,7 @@ static inline void update_sd_lb_stats(st > */ > if (prefer_sibling && !local_group && > sds->this && sds->this_stat.group_has_capacity) > - sgs->group_capacity = min(sgs->group_capacity, 1UL); > + sgs->group_capacity = min(sgs->group_capacity, 1U); > > /* Now, start updating sd_lb_stats */ > sds->total_load += sgs->group_load; > @@ -4896,7 +4924,7 @@ static struct sched_group *find_busiest_ > struct sg_lb_stats *this, *busiest; > struct sd_lb_stats sds; > > - memset(&sds, 0, sizeof(sds)); > + init_sd_lb_stats(&sds); > > /* > * Compute the various statistics relavent for load balancing at > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/